Thermal Consequences of Diurnal Microhabitat Selection in a Small Bird

Abstract

Thermal consequences of microhabitat selection during daily activity were quantified for male Phainopeplas Phainopepla nitens breeding during (1) spring in the Sonoran Desert, (2) summer in semiarid woodlands with mild, ocean-moderated climates, and (3) summer in semiarid woodlands isolated from ocean moderation. The interior woodland was markedly hotter during the Phainopepla's breeding season than were the other two habitats; for example, maximum air temperature averaged 39.70C in the interior woodland and 28-290C in the other two areas. Microhabitat selection was similar in the Sonoran Desert and the coastal woodland, but differed substantially between these locations and the interior woodland. Use of sites exposed to direct sunlight was reduced 56% in the interior woodland compared to the coastal location. This reflects reduced use of exposed perches with a resultant increase in use of shaded sites within vegetation which significantly lowers operative environmental temperatures experienced by birds in the interior woodland. Thus, site selection reduces by two-thirds the amount of time the animal experiences environmental temperatures above its upper critical temperature of 430C. Avoidance of exposed sites by birds breeding in the interior woodland may interfere with vital activities such as foraging and territorial advertisement.